mongo get avg cities from NY and CA

gistfile1.js

use test

db.zips.aggregate({
  $group : {
    _id : { state: '$state', city: '$city'}
    , totalPop : { $sum: '$pop' }
  }
},{
  $match : {
    totalPop: {$gte : 25000},
    $or: [{'_id.state': 'NY'}, {'_id.state': 'CA'}]
  }
}, {
  $group: {
    _id : "$_id.state",
    total: {$avg: '$totalPop'}
  }
}, {
  $group: {
    _id: "Total",
    total: {$avg: '$total'}
  }
});